This document relates to RF front-end module and antenna systems. Antenna structures having multiple resonating elements and multiple feeds may be configured so as to expand the operational bandwidths of a wireless device. In various examples, metamaterial-based components as well as non-metamaterial-based components may be utilized in the systems.
The propagation of electromagnetic waves in most materials obeys the right-hand rule for the (E,H,β) vector fields, considering the electrical field E, the magnetic field H, and the wave vector β (or propagation constant). The phase velocity direction is the same as the direction of the signal energy propagation (group velocity) and the refractive index is a positive number. Such materials are referred to as Right Handed (RH) materials. Most natural materials are RH materials.
A metamaterial has a structure that behaves as a metameterial, and is referred to as a metamaterial-based structure, and will be referred to herein as a metamaterial. When designed with a structural average unit cell size much smaller than the wavelength of the electromagnetic energy guided by the metamaterial, the metamaterial can behave like a homogeneous medium to the guided electromagnetic energy. Unlike RH materials, a metamaterial can exhibit a negative refractive index, and the phase velocity direction is opposite to the direction of the signal energy propagation, wherein the relative directions of the (E,H,β) vector fields follow the left-hand rule. Metamaterials which have a negative index of refraction with simultaneous negative permittivity ε and permeability μ are referred to as Left Handed (LH) metamaterials.
Many metamaterials are mixtures of LH metamaterials and RH materials and are referred to as Composite Right and Left Handed (CRLH) metamaterial, or CRLH structure, which may also be referred to as a CRLH-based structure. A CRLH structure may be designed to behave as an LH metamaterial at low frequencies and an RH material at high frequencies. Implementations and properties of various CRLH structures are described in, for example, Caloz and Itoh, “Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications,” John Wiley & Sons (2006). CRLH structures and their applications in antennas are described by Tatsuo Itoh in “Invited paper: Prospects for Metamaterials,” Electronics Letters, Vol. 40, No. 16 (August, 2004).
CRLH structures may be structured and engineered to exhibit electromagnetic properties tailored to specific applications and may be used in applications where it may be difficult, impractical or infeasible to use other materials. In addition, CRLH structures may be used to develop new applications and to construct new devices that may not be possible with RH structures alone.